Sea mark
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A sea mark is a pilotage aid which identifies the position of a maritime channel, hazard and administrative area to allow boats, ships and seaplanes to navigate safely.
There are two types sea mark:
- posts - fixed to the sea bed
- buoys - consisting of a floating object that is usually anchored to a specific location on the bottom of the sea or to a submerged object
Sea marks are used to locate channels, dangerous rocks or shoals, mooring positions, areas of speed limits, traffic separation schemes, submerged shipwrecks, and for a variety of other navigational purposes. Some are only intended to be visible in daylight (daymarks), others have some combination of lights, bells, horns, whistles and radar reflectors to make them usable in all weather conditions. Marks often display a number that is also noted on nautical charts.
The International Association of Lighthouse Authorities defines two systems of marks specifying the shapes, colours and characteristic lights of buoys depending on their purpose. For historical reasons, there are unfortunately two contradictory systems of lateral marks in use - IALA System B in the Americas, the Pillipines and Japan, and IALA System A everywhere else. The two systems differ principally in the colours used to denote the two sides of a channel. When approaching a harbour from seaward, System A places conical green marks to starboard and cylindrical red ones to port. In System B these are replaced with conical red marks to starboard and cylindrical green ones to port. This can be remembered (for System B) with the mnemonic "Red, right, return". Another System B mnemonic, which also helps with buoy numbering is "Even Red Left Port" (as in Eric the Red) - Even Numbered buoys are red, on your left (port) side leaving port.
See also: lightvessel, lighthouse, landmarkde:Seezeichen nl:Betonning